This invention concerns a new catalyst composition and its use for oligomerizing, particularly dimerizing and trimerizing, monoolefins. More particularly, it relates to combinations obtained by contacting, in any order, at least one bivalent nickel compound with at least one aluminum hydrocarbyl halide and at least one Bronsted organic acid.
It is already known to manufacture catalysts for dimerizing or codimerizing monoolefins such as ethylene, propylene or n-butenes. Among these catalysts, the following have been particularly described: the products formed by interacting .pi.-allyl nickel phosphine halides with Lewis acids (French Patent No. 1,410,430), the products formed by interacting phosphine nickel halides with Lewis acids (U.S. Pat. No. 3,485,881) and the products obtained by interacting certain nickel caboxylates with hydrocarbylaluminum halides (U.S. Pat. No. 3,321,546). Almost all of these catalysts are used in the presence of a ligand such as a phosphorus organic compound. As a matter of fact, it is desirable to make available oligomerization catalysts free of phosphorus. Other catalysts make use of zerovalent nickel compounds which are not of a very practical use in view of their instability and their high cost.
It has also been proposed to make use of catalysts wherein nickel is deposited on an inorganic carrier with acid sites, for example silica, silica-alumina, aluminum phosphate. These catalysts are in the solid phase, in contrast with the liquid phase catalysts according to the invention. Their activity is weak.
Finally, the prior art technique suffers from the following drawback: the continuous industrial operation of the known catalyst compositions for the treatment of olefin cuts such as those produced by petrochemical processes as the catalytic cracking or the steamcracking, raises some difficulties resulting, on the one hand, from the impurities contained in the cuts and, in the other hand, from an effective activity which is often smaller than in a closed vessel wherein all the constituents are introduced simultaneously at the beginning of the reaction and from the fact that said activity decreases with time.